Final answer:
Neptune's haze is a result of its internal heat source causing convection currents, which create additional clouds and visible structures, unlike the stable atmosphere of Uranus.
Step-by-step explanation:
Despite both Uranus and Neptune possessing similar atmospheric compositions, Neptune's atmosphere appears a bit hazy due to its internal heat source, which Uranus lacks. This internal heat in Neptune drives convection currents that lift warm gas above the 1.5-bar cloud level, forming additional clouds and introducing more dynamic atmospheric activity. Consequently, Neptune displays more visible structures such as bright white high-altitude clouds and the Great Dark Spot, both indicative of a more active atmospheric system compared to the relatively stable and featureless atmosphere of Uranus.